Coherence multiplexing in optics is known, allowing light reflected from an object to be decomposed, providing information on the location and magnitude of the various reflection sites within the object. This concept has been used in optics and other fields, including the medical community where it is used to interrogate the inner structures of the eye in optical coherence tomography (OCT).
A surface acoustic wave (SAW) is an acoustic wave traveling along the surface of a substrate material exhibiting elasticity, with an amplitude that decays exponentially with depth into the substrate material. Electronic devices employing SAWs typically use one or more interdigital transducers (IDTs) to convert acoustic waves to electrical signals and electrical signals to acoustic waves by using a thin metal film structure deposited on top of a piezoelectric crystal substrate to exploit the piezoelectric effect of certain materials (quartz, lithium niobate, lithium tantalate, lanthanum gallium silicate, etc.). The layout pattern of the input/output thin metal film patterns can be designed to provide the desired bandpass filtering function H(f)=Voutput/Vinput as the SAW propagates along the piezoelectric crystal surface. SAW devices are conventionally fabricated by deposition, photolithography and etch, the same processing used in the manufacture of conventional silicon-based integrated circuits.
SAW sensors are known for sensing a variety of physical, chemical and biological parameters. SAW sensors can provide delay lines, resonators, and devices with multiple frequency and time coded reflective structures. In single sensor systems, sensor identification is not required and therefore no encoding of the SAW device is required. In a multi-sensor system, the sensor is generally identified while simultaneously obtaining sensed information. Coherence multiplexing is not known in the field of SAW sensors.